This invention relates generally to the fumigation of grain and other commodities which are stored and/or shipped in bulk storage compartments. More specifically, this invention relates to improved method for the placement of fumigant in selected quantities and at selected locations within the depth of a bulk-stored commodity, particularly such as grain within the holds of seagoing vessels or other large storage compartments, wherein the fumigant produces toxic gases which penetrate the grain to exterminate pests therein, such as insects, rodents, and the like.
In the storage and/or shipment of grain and other bulk commodities, it is common practice to fumigate each storage compartment, such as the hold of a ship, by placing a quantity of gas-producing fumigant pellets or particles within the hold. The hold is then sealed whereby toxic gas produced by the fumigant is confined for contact with extermination of pests. The object of such fumigation techniques is to produce a lethal concentration of the toxic gas which will penetrate throughout the entire body of grain and to maintain that concentration for a sufficient period of time to exterminate all pests present.
A popular type of fumigant that has been in use for many years is a metallic phosphide, such as aluminum phosphide, which decomposes in the presence of water to from hydrogen phosphide, or phosphine, a toxic gas that has proven very successful as a fumigant. Reference is made to U.S. Pat. Nos. 2,826,486, 2,826,527, and 3,132,067 for details regarding fumigants of this general type in which the fumigant is normally provided in a solid form, such as tablets or pellets, activated by atmospheric moisture to produce the toxic gas and which decomposes into a residue of generally harmless powder.
Phosphine is poisonous not only to insects and rodents, but also to humans, such that great care must be exercised in its handling and use. In the context of ship hold fumigation, for example, workmen (longshoremen) will not enter a ship hold after fumigation has commenced. For this reason, the fumigant is normally placed into the hold after the grain or the like has been loaded by placing the fumigant at or near the upper surface of the grain, typically within compartmented bags of moisture- and gas-pervious material. These bags facilitate handling of the fumigant and are penetrated by moisture-laden air within the hold to initiate the gas-producing chemical reaction when the gases flow out of the bags into contact with the grain. The bags also contain the powder residue of the decomposed fumigant such that this residue can be easily separated from the grain, for example, at the shipping destination, thereby overcoming any fears regarding the presence of fumigant residues in the grain.
Normal air movement within the body of grain, however, tends to be in an upward direction. Accordingly, fumigant gases generated at or near the top of the grain may not penetrate downwardly a sufficient distance to reach the bottom of the storage compartment, which may have a substantial depth, such as typical shipping cargo holds having a depth on the order of about 60 feet. Moreover, sealing of ship cargo hatches is not always perfect, whereby toxic gases generated at or near the top of the grain frequently escape through the hatch opening without significant or full penetration through the body of the grain. As a result, fumigation techniques wherein the fumigant is placed near the top of the grain have not been completely satisfactory.
Although it would be highly desirable to place the fumigant in the bottom of a ship hold before grain is loaded thereinto, safety regulations prevent such procedure to prevent exposure of workmen within the hold to toxic gases during the loading process. Accordingly, some efforts have been made to provide devices permitting introduction of fumigant to a position substantially below the top surface of the grain after the loading process, for example, as in the apertured pipe shown in U.S. Pat. No. 4,059,048. In general, however, such pipe-type structures have not been completely successful probably in view of a chimney effect wherein toxic gases tend to congregate within the pipe at a position near the top of the grain.
There exists, therefore, a substantial need for an improved method and apparatus for fumigating grain or other bulk-stored commodities, wherein selected quantities of gas-producing fumigant can be placed quickly and easily at selected depths within a body of the commodity, such as grain, thereby achieving a more uniform and complete penetration through the commodity and a more effective resultant extermination of pests. The present invention fulfills this need and provides further related advantages.